The present invention relates to conventional guns that use propellant energy in combination with electromagnetic energy in a coil system that acts to launch projectile mass in the hypervelocity regime. Electromagnetic coil gun projectile launch systems are already known in the art. An example thereof is disclosed in: “Design and Performance of Sandia's Contactless Coilgun for 50 mm Projectiles,” IEEE Transactions on Magnetics, Vol. 29, No 1, p. 680, January 1993, R. J. Kaye et al and the entirety of which is incorporated herein by reference. An integrated propellant and coil gun system is disclosed in: “Hypervelocity Projectile Launching System,” U.S. patent application Ser. No. 13/916,176, 14 Jun. 2013, F. I. Grace et al, and the entirety of which is incorporated herein by reference.
It is known that extremely high magnetic fields can be obtained using high current levels that are passed through helically wire-wound coils. When a moving ferromagnetic or metallic material mass interacts with these magnetic fields, the mass is subjected to extremely high Lorentz forces. Such devices that employ these interactive forces are known as electromagnetic coilguns or launchers. In such coilgun, interaction of a metallic mass with an established magnetic field within the coil accelerates that mass. When the coil is energized with electrical current passing through its wires, the field induces a current within the metallic mass that in turn develops a magnetic field about the mass. Both coils and metallic mass have associated inductances. Inductance of the coil is proportional to the number of turns of wire in its windings, while that of the metallic mass corresponds to a single turn. There is also an established mutual inductance associated with the presence of both magnetic field-generating elements. The change in inductance as the interaction takes place and heat losses in the process establish the efficiency at which electrical energy is converted into mechanical or kinetic energy of the accelerated mass.
The force on the mass is described by J×B, which is the cross product of the current density vector J and magnetic field intensity vector B. When the coil is fixed in space, and an electrically conductive mass is initially placed at rest in close proximity to the coil, the mass may be accelerated either away from or towards the coil, depending on the sign of the changing electrical current in the coil. If the mass initially has a velocity, then the direction of current can either further accelerate the mass acting as an armature to greater velocity or alternately can retard the motion of the mass. Consequently, the coil system can act as an accelerator of mass being a linear electrical motor or a brake. The accelerating system converts electrical energy into kinetic energy whereas the decelerating system converts kinetic energy into electrical energy. Generally, a single coil having single or multiple windings is insufficient to provide large enough acceleration so several such coils are laid end to end along a central axis to compose a series of coil stages. By using a large number of coil stages the mass can be accelerated to very high velocity provided sufficient external electrical energy can be supplied to the coil stages. One example of a coil arrangement that can be employed in devices according to the invention is disclosed in the referenced Sandia article on coilguns. In addition, a large number of coil stages in the deceleration system could be used to reduce the initial velocity of the metallic mass to virtually zero.
Conventional propellants are routinely used to accelerate a projectile mass within a gun barrel [Army (February 1965), Interior Ballistics of Guns, Engineering Design Handbook: Ballistics Series, United States Army Material Command, AMCP 706-150, incorporated herein by reference]. The conversion mechanism and efficiency of chemical energy supplied by the propellant to projectile kinetic energy is well understood. There is an upper limit of velocity to which a projectile mass can be accelerated. Final velocity was limited by projectile mass, propellant mass, barrel length and the ability of the breech and barrel to withstand internal pressure from propellant combustion. Further, muzzle velocity is limited by the sound speed of the propellant gases that cause projectile acceleration. Since helium has higher sound speed than combustion gases, guns have been built wherein propellant combustion pressurizes a mass of helium and the pressurized helium accelerates the projectile. [Wikipedia.org/wiki/light_gas_gun: Light Gas Gun: Design Physics, 2013, incorporated herein by reference.]. Regardless of the amount of propellant used, type of gas used, barrel strength or length, or diminishing projectile mass, projectile velocity exiting the muzzle is limited in the prior art. With such limitation, gun design efficiency diminishes correspondingly as the theoretical limit is approached, i.e., progressively more propellant energy is wasted. These limits associated with the ability to produce higher projectile muzzle velocity have impeded advances in modern gun technology with regard to improvements in range, accuracy, hits against highly maneuvering targets, and lethality.
Electromagnetic launch of projectiles is not limited by the sound speed of gaseous products. Projectile velocity is limited by air resistance acting on the projectile in the barrel, maximum force that the coils can apply given the maximum currents supported by the projectile, and maximum magnetic fields that can be generated by the coils. Since anticipated projectile velocities, perhaps as high as 4 to 5 kilometers per second are far below these limiting factors, and since electromagnetic launch does not involve gases, there is no limiting factor for the cited velocity ranges of interest.
Projectile acceleration by a coil gun using single or multiple coils has been examined mainly to produce gun systems that do not rely on propellants. [Army Times: EM technology could revolutionize the mortar, 2011, incorporated herein by reference]. Launching a projectile mass from rest to the hypervelocity range requires a very large supply of electrical energy. The energy has to be delivered to the system within tens of milliseconds, which is commensurate with the length of the launch system and the time required for the projectile to traverse that length. The power source is external and massive while fast acting and relatively massive switching devices are required. The higher performing coilguns contain multiple coils that require additional fast acting switches as the projectile passes from one coil to another. An advantage over rail gun is that little friction, if any, is present between the projectile and the coil unlike the sliding and erosion prone electrical contacts used in railgun launch techniques. Power sources used are heavy magnetically braked rotating machinery and large capacitor banks that occupy large volumes of space. Such power sources cannot be easily accommodated by weapon platforms such as howitzers, tank-fired guns, or other smaller guns that require improvements.